Adjustable electromagnetic sound reproducer



W. A. BARTLETT ADJUSTABLE ELECTROMAGNETIC SOUND REPRODUCER Aug. 31 1926. 1,597,711

Filed Sept. 19. 1925 Mayra/a MAL/ICE 4. BARTLETT BX dz 1?.

ATTORNEK Patented Aug. 31, 1926.

UNITED STATES 1,597,711 PATENT OFFICE.

\VALLAGE A. BARTLETT, OF LONDON, ENGLAND, ASSIGNOR TO BRANDES LABORA- TORIES, INC., OF NEWARK, JERSEY, A CORPORATION OF NEW JERSEY.

ADJ USTABLE ELECTROMAGNETIC SOUND REPRODUCER.

Application filed September 19, 1925.

This invention relates broadly to electromagnetic sound reproducers, or loud SIJPtIkQl'S, as used in radio broadcast recept on. and more particularly to a construction iv of loud speaker wherein the magnetic gap between the driver and the sound reproduciug diaphragm may be readily varied.

The principal objects of the invention are, to facilitate the assembly of the several parts 1 comprising the loud speaker by means particularly suitable for use in mass production while providing, if desired, for the relative adjustment of the diaphragm and the magnet pole pieces; and to improve the tone quality of the instrument, mainly by eliminating undesirable vibration between the assembled parts.

1 provide an electromagnetic sound reproducer, in which the horn supporting means and the casing carrying the electromagnetic mechanism are assembled and secured to the base by the aid of a sleeve or sleeve member common to both. The arrangement is such that the horn supporting means is firmly seated and rigidly attached to the base, so that no vibration, which may be set up when said means is clamped to the base by the usual clamping ring as has been the practice heretofore in the art, can occur between these two parts; but the acoustic advantages which I have found can be obtained with a reproducer in which the horn is set vertically downwards in the base are fully retained.

Preferably, an externally screw threaded sleeve is used, the same being screwed into a cup attached to the horn ferrule anl secured to the base by a clamping nut. This construction enables the casing for the electromagnetic means to be screwed on the lower end of the sleeve in such manner that it can be adjusted.

A resilient washer is, or may be, interposed between the casing and the clamping nut to ensure a steady adjustment without requiring such accuracy in the screw threaded connections as would hinder mass production.

Experiments have shown that the acoustic properties of an instrument of the character to which the present invention applies are greatly improved by mounting the diaphragm between a pa1r of annular rings each made up of a'fabric sheet and a rubber film. Such a mounting in conjunction with Serial No. 57,457.

Fig. 1 shows the reproducer in sectional elevation; and Figs. 2 and 3 are respectively an elevation and a plan of the resilient washer already mentioned.

Reference 4 denotes the base (of metal), 5 denotes the cap (of hard rubber) for the horn supporting ferrule, 6 the ferrule itself, 7 the horn (of non-resonating material) supported thereby, and 8 the casing containing the electromagnetic mechanism.

A11 annular skirt 9 depends from the cap 5 and is screw threaded internally for its attachment to the base 4: in a manner to be described. The cap 5 is also made with a depending annular ring 10 on its lower face, to serve as a seat for the diaphragm 12 of the electromagnetic mechanism, and with a thickened central portion having an upper annular flange 11 on which a shoulder on the ferrule 6 seats when the ferruleis screwed into the central screw threaded opening in the cap. To ensure that the shoulder will seat firmly on the flange the screw threaded opening is counterbored, as shown, immediately adjacent the flange.

Screwed into the skirt 9 of the cap 5 is an externally screw threaded sleeve 13. This sleeve has a fourfold purpose. It clamps the diaphragm 12 between its upper end and the depending ring 10 of the cap, it serves for the attachment of the cap to the base 4, it serves also for the attachment of the casing 8, and it enables said casing to be turned for the purpose of adjusting the pole pieces 1& relatively to the diaphragm 12.

After the sleeve 13 has been screwed into the cap 5, the cap isset vertically downwards on the upper flange 15 of the base 4,

with the sleeve depending through the central opening in said base, and it is then clamped to the base by means of a nut 16 threaded on the sleeve.

The casing 8, after the electromagnetic mechanism has been assembled therein, is threaded on to the lower part of the sleeve,

a resilient washer 17 being interposed between the casing and the nut 16.

As shown in Figs. 2 and 3, this washer consists of a ring of sheet metal having portions slit and pressed upto form resilient tongues 18. I

A stud 19 projects from the centre of the casing, and a handle 20 is attached, by means of a nut 21 and spring washer 22, to said stud, the handle being retained in place by a pop mark 23 on its upper surface pressing into one of a number of serrations in the lower surface of the casing radiating from the stud hole. With this arrangement the handle. can be quickly fixed in the desired position after the correct initial position of the casing 8 on the sleeve 13 has been determined. The handle extends through an arcuate slot in the base 4 and terminates in a grip 25, the length of the slot being sufiicient to give a movement of the handle of approximately 120.

By moving the handle along the arcuate slot in the base, the casing 8 will be partially rotated on the sleeve 13, thereby adjusting the relative positions of the pole pieces 14 and the diaphragm 12. The pressure exerted by the tongues 18 of the Washer 17 takes up any play between the threads of the casing and of the sleeve, enables a firm, even adjustment to bemade, and prevents longitudinal vibration of the pole pieces 14 of the electromagnetic mechanism.

The electromagnetic mechanism includes magnet coils 26, wound on the pole pieces. 14, and permanent magnets 27 located around the interior of the casing 8. The permanent magnets are shown maintained in position by kidney pieces 28 secured to the casing by means of screws 30. The terminals from the magnet windings are brought out to binding posts 31.

The diaphragm 12 is shown mounted between a pair of annular rings 32, 33, each of which is made up of two dissimilar materials, namely, a fabric sheet and a rubber film moulded together or combined in an integral solid body. Both the fabric and the rubber are extremely thin. The rubber surface is placed immediately adjacent the diaphragm 12 whereas the fabric surfaces contact with the ring 10 and the upper end of the sleeve 13. The rubber film resiliently supports the diaphragm and permits relatively large vertical movement of the same.

Various changes in detail may be made without departing from the spirit or scope of the invention as defined by the claims which follow. In some cases, for example, where it may be desirable to reduce manufacturi g expense, the casing 8 may? be fixed in place on the sleeve 13, the adjusting handle 20 and appertaining parts then being omitted as unnecessary.

: What I c1ai m and desir, to secure by member, said capmember having a substantially flat annular flange around its lower periphery for engagement with the top face of said base, a locking nut engaging said screw threaded sleeve member beneath the top portion of said base for securing said screw threaded sleeve member rigidly with respect to said base, an internally screw threaded cup shaped caa'ng arranged to engage the lower portion of said screw threaded sleeve member, and an electromagnetic driving mechanism contained within said cup shaped casing for actuating said sound reproducing diaphragm.

2. An electromagnetic sound reproducer comprising in combination a centrally apertured supporting base, a screw threaded sleeve member, a sound reproducing diaphragm supported upon the upper peripheral edge of said screw threaded sleeve member, a cap engaging said screw, threaded sleeve member and having a flat annular flange arranged to contact with the top of said centrally apertured supporting base, a nut arranged to engage said screw threaded sleevemember and grip the under surface of said centrally apertured base, a cup-shaped casing containing electromagnetic driving mechanism, internal screw threads in said cup-shaped casing arranged to engage with the screw threads on said sleeve member, and an operating lever for imparting rotative movement to said cupshaped casing for varying the distance be-' tween said electromagnetic driving mechanism and said sound reproducing dia phragm.

3. An electromagnetic sound reproducer comprising in combination a centrally apertured supporting base, a screw threaded sleeve member, a. sound reproducing diaphragm supported upon the upper peripheral edge of said screw threaded sleeve member, a cap engaging said screw threaded sleeve member and having a flat annular flange arranged to contact with the top' of said centrally apertured supporting base, a nut arranged to engage said screw threaded sleeve member and grip the under surface of said centrally apertured base, a. cup

; shaped casing" containing electromagnetic driving mechanism, internal screw threads 1n said cup shaped casing arranged to en gage with the screw threads on said sleeve said casing for advancing or retracting said member, a resilient washer member dis-' easingfon said screw threaded sleeve memposed between the under surface of said nut her for varying the distance between said 10 and the upper peripheral edge of said cup electromagnetic driving mechanism and said I shaped casing for preventing play between sound reproducing diaphragm.

said casing and said sleeve member, and means for imparting rotative movement to WALLACE A. BARTLETT. 

